Formation of Fischer-type aminocarbenes by a double C-H bond activation of a methylamino group

Article abstract of DOI:10.1021/om060314g

The reaction at room temperature of [RuCl₂(PPh₃) ₃] and the ferrocenyl aminophosphine ligand PAPF leads to the product [RuCl₂(PPh₃)(PAPF)], 1c, in equilibrium with the starting materials. A shift of the reaction toward the formation of le was observed with temperature. At 130°C, le was transformed into the chelate aminocarbene complex [RuCl₂(PPh₃)(PAPF-c)], 2, after a double C-H activation of the aminomethyl fragment. Complex 2 exhibits in the solid state a strong agostic interaction (X-ray structure determination) that is also maintained in solution. An intermediate of the transformation of 1 into 2 has been observed in solution. When complex 2 is heated in DMSO, displacement of the PPh₃ ligand by DMSO takes place, while the agostic interaction remains unchanged. The similar complexes [RuCl₂-(PPh ₃)(PN)], with the ligand PPFA or PTFA, did not undergo any transformation upon heating and the aminocarbene group was not formed.

Full text of DOI:10.1021/om060314g

4498
Organometallics 2006, 25, 4498-4503
Formation of Fischer-Type Aminocarbenes by a Double C-H Bond
Activation of a Methylamino Group
M. Carmen Carrio´n,† Ernesto Garc´ıa-Vaquero,† Fe´lix A. Jalo´n,† Blanca R. Manzano,*,†
Walter Weissensteiner,‡ and Kurt Mereiter§
Departamento de Qu´ımica Inorga´nica, Orga´nica y Bioqu´ımica-IRICA, UniVersidad de Castilla-La
Mancha, AVenida C. J. Cela, 10, 13071 Ciudad Real, Spain, Institut fu¨r Organische Chemie, UniVersita¨t
Wien, Wa¨hringer Strasse 38, A-1090 Vienna, Austria, and Department of Chemistry, Vienna UniVersity of
Technology, Getreidemarkt 9/164SC, A-1060 Vienna, Austria
ReceiVed April 7, 2006
The reaction at room temperature of [RuCl2(PPh3)3] and the ferrocenyl aminophosphine ligand PAPF
leads to the product [RuCl2(PPh3)(PAPF)], 1c, in equilibrium with the starting materials. A shift of the
reaction toward the formation of 1c was observed with temperature. At 130 °C, 1c was transformed into
the chelate aminocarbene complex [RuCl2(PPh3)(PAPF-c)], 2, after a double C-H activation of the
aminomethyl fragment. Complex 2 exhibits in the solid state a strong agostic interaction (X-ray structure
determination) that is also maintained in solution. An intermediate of the transformation of 1 into 2 has
been observed in solution. When complex 2 is heated in DMSO, displacement of the PPh3 ligand by
DMSO takes place, while the agostic interaction remains unchanged. The similar complexes [RuCl2-
(PPh3)(PN)], with the ligand PPFA or PTFA, did not undergo any transformation upon heating and the
aminocarbene group was not formed.
is restricted to laborious methods that limit the applicability of
these systems. In principle, a reasonable way to prepare chiral
aminocarbenes is through the double C-H activation of
methylamino derivatives, but the direct activation of methyl
groups to give aminocarbenes is a difficult process that has only
rarely been reported in the literature,4 with the exception of
studies involving carbonyl clusters of Os.5 Although difficult,
it seems more favorable to convert alkenes,6 THF,7 aldimines,
and aminals or amides8 to carbenes. The formation of ami-
nocarbenes by the attack of a nitrogen atom at the R carbon of
a Ru-vinylidene moiety has also been described.9 The difficulty
in transforming an aminomethyl group to an aminocarbene arises
due to the need for double C-H activation of the aminomethyl
Introduction
The preparation of chiral aminocarbenes is an important goal
in organic synthesis and catalysis.1 In particular, the preparation
of chiral N-heterocyclic carbenes (NHC) and their application
in the synthesis and study of the reactivity of metallic complexes
is a current and very active research field. Indeed, a relatively
large number of results can be found in this area in the
literature.2 Such metallic carbenes have been widely tested in
catalytic reactions.3 In contrast to this significant activity, the
preparation of more classical chiral Fischer-type aminocarbenes
This paper is dedicated to Prof. Victor Riera on the occasion of his
70th birthday.
* To whom correspondence should be addressed. E-mail:
blanca.manzano@uclm.es.
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Int. Ed. 2004, 43, 5130. (h) Perry, M. C.; Burgess, K. Tetrahedron:
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† Universidad de Castilla-La Mancha.
‡ Universita¨t Wien.
§ Vienna University of Technology.
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10.1021/om060314g CCC: $33.50 © 2006 American Chemical Society
Publication on Web 08/09/2006

Formation of Fischer-Type Aminocarbenes
Organometallics, Vol. 25, No. 19, 2006 4499
Chart 1
Results and Discussion
Synthesis. As reported previously14,15 the reaction of [RuCl2-
(PPh3)3] with PPFA or PTFA in toluene at room temperature
leads to complexes with the formula [RuCl2(PPh3)(PN)] together
with free PPh3 (first step in Scheme 1, PN ) PPFA, 1a; PTFA,
1b). When the reaction was carried out in refluxing toluene,
the complexes [RuCl2(PPh3)(PN)] were recovered as the sole
products. The same result was obtained upon heating solutions
of the isolated complexes. Consequently, activation of the
aminomethyl group was not observed.
group. In principle, the process could start with an initial agostic
C-H‚‚‚metal interaction that, after C-H activation, would lead
to an alkylhydride intermediate. This intermediate should evolve
selectively toward a second C-H activation. This mechanistic
route has been demonstrated for one Ru complex10 but seems
to be a difficult process in the majority of metallic systems. Ru
complexes are known to form easily agostic C-H‚‚‚Ru interac-
tions11 and to stabilize the intermediates of an NC-H12 and
even a double NC-H bond activation.13
On the basis of the information outlined above, the goal of
the present work was the preparation of Fischer-type aminocar-
bene derivatives from unsaturated 16-electron chiral Ru com-
plexes of formula [RuCl2(PPh3)(PN)], where PN are the
aminophosphine ligands derived from ferrocene (see Chart 1).
The corresponding complexes with this formula bearing PTFA14
and PPFA15 ligands have been prepared previously by ourselves
and other authors. Formally, a double CH activation of the
methylamino groups of these compounds could lead to the
formation of the aforementioned aminocarbenes. The ligands
shown in Chart 1 are similar in terms of the relative dispositions
of the P and N donor ligands but differ in the rigidity of the
backbone. The ligands are arranged in Chart 1 from the least to
the most rigid structure according to our experience in the NMR
analysis in solution of different Pd and Ru complexes.14,16 The
ability of the ferrocenyl fragments to stabilize carbenes, both
of the Fischer17 and the N-heterocyclic3i,18 types, was demon-
strated in previous studies.
Different results were obtained when the more rigid ligand
PAPF was used. The reaction between [RuCl2(PPh3)3] and PAPF
at room temperature gave the product [RuCl2(PPh3)(PAPF)],
1c but this was in equilibrium with the starting materials (see
Scheme 1). The existence of such an equilibrium was confirmed
by monitoring the relative ratios of 1c and the free ligands PPh3
and PAPF in the 31P NMR spectra between 90 and 20 °C. The
reaction mixture was initially heated at 90 °C, and the
equilibrium constant was determined at this temperature. The
equilibrium constants were also determined at 80 and 60 °C
(see Experimental Section). A clear shift in the reaction toward
the formation of 1c and free PPh3 was observed when the
temperature was higher. Consequently, the temperature of the
reaction medium was increased in order to favor the formation
of 1c or even activate the methyl group. When the reaction was
monitored by 31P and 1H NMR spectroscopy, chemical changes
were not observed up to 100 °C. However, at 110 °C the slow
transformation of 1c to give the chelate aminocarbene 2 was
observed. Given this information, the reaction was carried out
at 130 °C in a closed Fisher-Porter tube in which this
temperature could be achieved in toluene. Under these condi-
tions, 2 was formed in excellent yield after 12 h. However, under
these conditions the complexes 1a and 1b did not undergo any
transformation.
To shed light on the mechanism of this process, we monitored
this reaction in toluene-d6 by 1H NMR spectroscopy at 110 °C
during 6 h. This experiment, together with the 31P NMR
resonances of 1c and 2, provides evidence for the presence of
a minor component in the reaction medium. The spectrum
showed three mutually coupled resonances, two with a JPP
constant typical of phosphines in a mutually trans arrangement
(see Figure 1). In the 1H NMR spectrum, apart from 1c, evidence
for another complex with coordinated dimethylamino groups
was not found. We propose that this minor component is [RuCl2-
(PPh3)2(κ1-P-PAPF)], I (the disposition of the ligands proposed
in Scheme 2 is speculative), and this could be formed from 1c
by displacement of the NMe2 group by PPh3. It is interesting
to note that in this intermediate the NMe2 group could be able
to contact the Ru center and undergo the two necessary C-H
activations that would give rise to 2. A reasonable but
speculative mechanism for the change from 1c to 2 is depicted
in Scheme 2. After decoordination of the dimethylamino group
in 1c, the rigidity of the ligand would probably allow this group
to be in close proximity to the unsaturated metal center and the
formation of a MeNCH2-H‚‚‚Ru agostic interaction would be
possible (formation of II). Subsequent oxidative addition could
lead to an alkyl hydride (III), and thissafter a second C-H
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4500 Organometallics, Vol. 25, No. 19, 2006
Carrio´n et al.
Scheme 1
Scheme 2
Scheme 3
achieved. It is worth noting that the agostic interaction in
complex 2 is not replaced by DMSO even at high temperature.
Furthermore, the displacement of a strong donor ligand such
as PPh3 takes place with the agostic interaction remaining
unaffected. This reflects a high stability of the moiety “Ru-
(PAPF-c)”.
The different behavior exhibited by the PAPF ligand when
compared with the other two is worthy of note. The complexes
[RuCl2(PPh3)(PN)] with PPFA and PTFA seem to be highly
stable. In the case of PAPF, a lower coordinating ability is
observed for the ligand if we take into account the existence of
the equilibrium in the formation of 1c and the detection at high
temperature of a species in which the dimethylamino group is
uncoordinated. As previously stated, this lack of coordination
would allow the activation of the methylamino group. It is
possible that the steric requirements of the PAPF ligand related
to its rigid backbone could be the origin of the relative tendency
of the NMe2 group of complex 1c to become decoordinated.
Besides, as stated above, the rigidity of the ligand backbone
could allow access of this group to the metal center and this
could, in turn, be activated.
activation (formation of IV) and H2 liberationswould form the
aminocarbene fragment of 2, which also exhibits an agostic
interaction (see below).
When 2 was dissolved in DMSO-d6, a transformation was
not observed at room temperature or even after heating 1 h at
55 °C. However, at 75 °C a slow transformation began to take
place. A new product, 3, appeared, and after 2 h at 95 °C the
ratio 2:3 was 6:7. According to the NMR studies (see below),
3 may be formulated as [RuCl2(DMSO-d6)(PAPF-c)] (PAPF-c
) aminocarbene derived from PAPF) formed after the replace-
ment of PPh3 by DMSO-d6, with the coordination mode of the
ferrocenyl ligand unchanged (see Scheme 3). The transformation
between 2 and 3 is reversible and 3 reverts slowly in the NMR
tube to give 2 when the temperature is lowered. After 2 days at
room temperature, the ratio 2:3 is 9:7, while after 4 days it is
2:1, indicating that probably the equilibrium ratio has not been
Structural Characterization. Complexes 1c, 2, and 3 were
characterized in solution by 1H and 31P{1H} NMR spectroscopy
(also by 13C{1H} in the case of 1c and 2). A complete
assignment of the resonances was possible thanks to techniques
1
1
such as bidimensional H-1H and H-13C g-HSQC, selective
31P decoupled 1H NMR spectra, monodimensional NOE experi-
ments, and consideration of the characteristic pattern of these
types of complexes (see information in Experimental Section).
If the 1H and 13C{1H} NMR data for 1c and 2 are compared,
one significant difference is observed concerning the number
of aminomethyl groups, and this is apparent for both nuclei.
Two different groups are observed for 1c, and this is due to the
coordination of the N donor atom, which makes the two methyl
groups diastereotopic. In contrast, only one type of methyl group
is observed for 2. For this complex a characteristic carbene
1
resonance is observed in the H NMR spectrum at 8.93 ppm,
which integrates as one proton, and at 252.91 ppm in the 13C-
{1H} NMR spectrum. Another salient difference in the 1H NMR
spectra of these complexes is the existence in 2 of a resonance
Figure 1. 31P{1H} NMR spectra (toluene-d6, 110 °C) corresponding
to the transformation of 1c into 2.

Formation of Fischer-Type Aminocarbenes
Organometallics, Vol. 25, No. 19, 2006 4501
at -3.62 ppm, which can be attributed to one of the H2′′ protons
of the chain of the PAPF ligand. This anomalous chemical shift
can be explained by the existence of an agostic interaction with
the corresponding C-H bond. In the 13C{1H} NMR spectrum,
the carbon resonance of this bond appears at 46.86 ppm as a
triplet with a JCP of 16.5 Hz. In the proton-coupled 13C NMR
spectrum this signal exhibits two different JCH coupling constants
of 138.3 and 103.3 Hz. The former value is comparable to that
3
expected for a conventional alkylic CH bond (for instance JCH ′′
) 130 Hz), but the reduction in the latter value must be due to
the agostic interaction. This indicates that the agostic interaction
for one of the C-H bonds of the C2′′H2 unit, which is observed
in the solid state (see below), is maintained in solution. In the
1H NMR spectra, both complexes show the expected seven
resonances for the Cp protons, but a noteworthy difference is
observed: a shift to low frequency (2.14 ppm) of one of the
resonances in 1c but not in 2. This difference is due to the
conformation that the ligand is forced to adopt when it is P,N-
bidentate. As described previously,16,19 when this ligand (or
similar diphosphines) are coordinated to a transition metal in a
chelate fashion, one phenyl ring of the diphenyl phosphino group
is forced to be in close proximity to Cp2 and this is very effective
at shielding the cyclopentadienyl H5′ proton of this ring. As a
result, this signal appears at very low frequency (δ ) 2-2.7
ppm). This anomalous chemical shift indicates chelate P,N-
coordination of the ligands and also reflects their high level of
rigidity. In the free ligands the signal for this proton appears in
the normal range for cyclopentadienyl protons. The absence of
this high-field shift for H5′ in the case of 2 reflects a different
conformation of the diphenylphosphino unit in this complex.
In the case of 2, several phenylic resonances appear broad. For
instance, at room temperature one ortho proton resonance of
the ferrocenyl PPh2 group is broad, while the other is sharp.
The former signal is resolved as a defined triplet when the
sample is heated to 45 °C. This indicates the possibility that
steric hindrance exists in the complex, and this prevents
complete free rotation of the phenylic ring of the ferrocenyl
ligand.
Figure 2. Structural view of 2 showing 30% displacement
ellipsoids (aromatic and CH3 hydrogen atoms and CH2Cl2 molecules
omitted for clarity). Selected bond lengths and angles (Å, deg):
Ru-C(14) 1.957(3), Ru-P(1) 2.349(1), Ru-P(2) 2.267(1), Ru-
Cl(1) 2.509(1), Ru-Cl(2) 2.475(1), Ru-C(12) 2.644(3), Ru-
H(12a) 1.919, P(2)-Ru-C(14) 93.26(8), P(2)-Ru-P(1) 100.01(3),
P(2)-Ru-Cl(1) 99.34(3), P(2)-Ru-Cl(2) 85.52(3), P(2)-Ru-
H(12a) 176.1, C(14)-Ru-H(12a) 88.5, Ru-H(12a)-C(12) 128.6.
resonance in 2. This fact can be interpreted in terms of the high
donor ability of these P donor centers. In the case of 1c, and
according to the known structure of the analogous complex
[RuCl2(PPh3)(iso-PFA)] [iso-PFA ) (η5-C5H5)Fe(η5-C5H3-
(CHMeNMe2)P(i-Pr2-1,2)],20 a distorted square pyramidal ge-
ometry is expected. If the P atom of the PPFA ligand is located
in the apical position (similar to the aforementioned complex),
the P atom should be a strong donor center. In 2 the P atom of
the ferrocenyl ligand is disposed trans to the weak donor agostic
interaction, as evidenced by the X-ray structure (see below). In
both cases, a shift to higher frequencies is expected for these P
atoms.
1
The H NMR spectrum of 3 is quite similar to that of 2.
In the case of 3, only a singlet is observed in the 31P{1H}
NMR spectrum, and this is in accordance with the proposed
displacement of the PPh3 ligand. The absence of coordination
in the PPh3 unit was confirmed by the fact that couplings did
Comparable signals are observed for the ferrocenyl ligand,
although changes in the chemical shifts are observed. This shift
is considerable in the case of the aminomethyl group (about
0.5 ppm) and in the carbene and agostic protons (about 2 ppm).
As expected, the coupling of these protons with the phosphorus
atom of PPh3, as observed in the case of 2, is not seen in 3.
The steric hindrance in this derivative seems to be less marked
than in 2 because the ortho phenylic signal, which is separated
from the rest, appears as a well-defined multiplet that is
transformed into an apparent doublet after decoupling of the
PAPF-c phosphorus.
1
not disappear in the H NMR spectrum of 3 after selective
irradiation of the free PPh3 resonance.
As we were not able to isolate 3 in a pure form, we performed
a MALDI mass spectrum of a mixture of 2 and 3 (see
Experimental Section). Fortunately, a peak corresponding to 3
after the loss of one chloride was clearly observed.
X-ray Diffraction Analysis for 2‚2CH2Cl2. The X-ray
crystal structure of the solvate 2‚2CH2Cl2 consists of a neutral
Ru complex with two CH2Cl2 molecules of crystallization per
complex. The molecular structure of 2 is presented in Figure 2
with the atom-labeling scheme and a selection of bond lengths
and angles. Two chlorides, a PPh3, and a phosphinoaminocar-
bene ligand, PAPF-c, are coordinated to the Ru atom. This is
consistent with the proposed double C-H activation experienced
by PAPF, which is transformed in this way into a chelating
phosphinoaminocarbene. Importantly, an agostic interaction
completes the coordination sphere of Ru, and this environment
is a distorted octahedron. Although some examples of agostic
interactions in complexes with NHC ligands have been
The 31P{1H} NMR spectra of compounds 1c and 2 at room
temperature are characterized by the presence of two doublets
corresponding to the two nonequivalent phosphines arranged
in a cis disposition. One of the resonances is shifted to
significantly higher frequency as compared to the other.
1
According to the selectively 31P-decoupled H NMR spectra,
these signals correspond to the PAPF in 1c and the PPh3
(19) (a) Carrio´n, M. C.; Jalo´n, F. A.; Lo´pez-Agenjo, A.; Manzano, B.
R.; Weissensteiner, W.; Mereiter, K. J. Organomet. Chem. 2006, 691, 1369.
(b) Jalo´n, F. A.; Manzano, B. R.; Go´mez-de la Torre, F.; Lo´pez-Agenjo,
A. M.; Rodr´ıguez, A. M.; Weissensteiner, W.; Sturm, T.; Mah´ıa, J.; Maestro,
M. J. Chem. Soc., Dalton Trans 2001, 2417 (c) Mernyi, A.; Kratky, C.;
Weissensteiner, W.; Widhalm, M. J. Organomet. Chem. 1996, 508, 209.
(d) Sturm, T.; Weissensteiner, W.; Mereiter, K.; Ke´gl, T.; Jeges, G.; Petolz,
G.; Kolla´r, L. J. Organomet. Chem. 2000, 595, 93.
(20) Hampton, C. R. S. M.; Butler, I. R.; Cullen, W. R.; James, B. R.;
Charland, J. P.; Simpson, J. Inorg. Chem. 1992, 31, 5509.

4502 Organometallics, Vol. 25, No. 19, 2006
Carrio´n et al.
described,3i,21 to the best of our knowledge 2 is the first example
in which a Fischer-type aminocarbene ligand also exhibits an
agostic interaction. Taking into account the origin of the
aminocarbene group, this interaction can be considered as the
beginning of a third C-H activation. Such interactions have
also been described in RuCl2L3 complexes.3i,22 Two agostic
interactions have been observed in RuCl2L2 complexes,23 and
two nonclassical agostic interactions (involving two C-H bonds
of each methyl group) have been described24 in RuCl2[PPh2-
(2,6-Me2C6H3)]2. Other examples include cationic derivatives
of the type25 [RuXL4]+ or26 [RuXL3]+ and clusters or dimetallic
complexes.27 The relatively short Ru-C(12) [2.644(3) Å] and
Ru-H(12a) (1.919 Å) distances indicate that the agostic
interaction is strong.23,24,26b
located below the upper Cp ring and the phenyl group is no
longer orientated toward the lower Cp ring (see Figure 2). This
situation is consistent with the chemical shifts found for the
H5′ proton in 1 and 2, as explained in the NMR section (see
above).
In conclusion, we have been able to transform a dimethyl-
amino group into an aminocarbene in a PAPF Ru complex. The
idea that an uncoordianted methylamino group forced to be in
close proximity to an unsaturated center could give rise to an
aminocarbene unit may lead to future developments in this field.
The new aminocarbene complex obtained contains a very stable
agostic interaction that is not displaced by DMSO at high
temperature. Instead, the PPh3 ligand is substituted by the
coordinating solvent.
The PPh3 ligand is trans to this agostic interaction, and this
makes the Ru-P(2) bond distance particularly short [2.267(1)
Å] as compared with the Ru-P(1) bond distance of 2.349(1)
Å. This structural information is consistent with the chemical
shift of the PPh3 group in the 31P NMR spectrum.
As far as the aminocarbene unit is concerned, the Ru-C(14)
[1.957(3) Å] and C(14)-N [1.309(3) Å] bond distances and
the Ru-C(14)-N [122.9(2)°] angle are in the expected range
for this type of Ru carbene compounds (Ru-C distances are
usually in the range 1.91-2.04 Å, N-C in the range 1.26-
1.36 Å, and Ru-C-N angles in the range 115-142°).8a,b,9,28
The transformation of the aminomethyl group into the
aminocarbene fragment leads to significant changes in the
conformation of the coordinated ferrocenyl ligand. The apical
orientation of the dimethylamino group (or the PR2 groups in
the analogous diphosphine ligands) (see Chart 1) means that
the metal is clearly located above the upper Cp plane. This forces
the phosphorus atom to orientate the electron pair toward the
metal position by rotating the PPh2 unit about the C(Cp)-P
bond, which at the same time places one phenyl ring in close
proximity to the lower Cp ring.16,19 In the carbene ligand,
coordination through the carbon atom means that the metal is
Experimental Section
General Procedures. All manipulations were carried out under
an atmosphere of dry oxygen-free nitrogen using standard Schlenk
techniques. Solvents were predried and distilled over appropriate
drying agents and degassed before use.
1H, 13C{1H}, and 31P{1H} spectra were recorded on Varian
1
UNITY INOVA 500 and Varian UNITY 300 spectrometers. H
NMR spectra selectively decoupled from 31P were also registered.
Coupling constants are in Hz. Chemical shifts (ppm) are given
relative to TMS (1H, 13C NMR), taking as reference the signal of
the deuterated solvent that has been used. For the 31P NMR, H3-
1
PO4 (85%) has been used as reference. H-1H COSY spectra:
standard pulse sequence with an acquisition time of 0.214 s, pulse
width 10 ms, relaxation delay 1 s, number of scans 16, number of
increments 512. The NOE difference spectra: recorded with 5000
Hz, acquisition time 3.27 s, pulse width 90°, relaxation delay 4 s,
1
irradiation power 5-10 dB. H-13C g-HSQC spectra: standard
pulse sequence with an acquisition time of 0.1 s, pulse width 11
ms, relaxation delay 1 s, number of scans 8, number of increments
256. Elemental analyses were performed with a Perkin-Elmer 2400
microanalyzer. The MALDI mass spectra was recorded in a Bruker
MicroFlex. s ) singlet, d ) doublet, t ) triplet, m ) multiplet, b
) broad. If not specified, the 13C{1H} NMR resonances are singlets.
RuCl2(PPh3)329 was prepared according to literature, and the ligands
PPFA,30 PTFA,31 and PAPF19c were prepared as previously
described.
(21) (a) Burling, S.; Kociok-Ko¨hn, G.; Mahon, M. F.; Whittlesey, M.
K.; Williams, J. M. J. Organometallics 2005, 24, 5868. (b) Abdur-Rashid,
K.; Fedorkiw, T.; Lough, A. J.; Morris, R. H. Organometallics 2004, 23,
86.
(22) (a) La Placa, S. J.; Ibers, J. A. Inorg. Chem. 1965, 4, 778. (b)
Goicoechea, J. M.; Mahon, M. F.; Whittlesey, M. K.; Kumar, P. G. A.;
Pregosin, P. S. Dalton Trans. 2005, 588. (c) Major, Q.; Lough, A. J.; Gusev,
D. G. Organometallics 2005, 24, 2492.
(23) Baratta, W.; Herdtweck, E.; Rigo, P. Angew. Chem., Int. Ed. 1999,
38, 1629.
(24) Baratta, W.; Mealli, C.; Herdtweck, E.; Ienco, A.; Mason, S. A.;
Rigo, P. J. Am. Chem. Soc. 2004, 126, 5549.
(25) (a) Bennett, M. A.; Goh, L. Y.; McMahon, I. J.; Mitchell, T. R. B.;
Robertson, G. B.; Turney, T. W.; Wickramasinghe, W. A. Organometallics
1992, 11, 3069. (b) Teixidor, F.; Ayllo´n, J. A.; Vin˜as, C.; Kivekas, R.;
Sillanpaa, R.; Casabo, J. Chem. Commun. 1992, 1281. (c) Jime´nez-Tenorio,
M.; Mereiter, K.; Puerta, M. C.; Valerga, P. J. Am. Chem. Soc. 2000, 122,
11230.
(26) (a) Huang, D.; Huffman, J. C.; Bollinger, J. C.; Eisenstein, O.;
Caulton, K. G. J. Am. Chem. Soc. 1997, 119, 7398. (b) Huang, D.; Streib,
W. E.; Bollinger, J. C.; Caulton, K. G.; Winter, R. F.; Scheiring, T. J. Am.
Chem. Soc. 1999, 121, 8087.
(27) (a) Brown, D. B.; Cripps, M.; Johnson, B. F. G.; Martin, C. M.;
Braga, D.; Grepioni, F. Chem. Commun. 1996, 1425. (b) Kuhlman, R.;
Streib, K.; Caulton, K. G. J. Am. Chem. Soc. 1993, 115, 5813. (c) Kuhlman,
R.; Folting, K.; Caulton, K. G. Organometallics 1995, 14, 3188. (d) Zhongli,
H.; Plasseraud, L.; Moldes, I.; Dahan, F.; Neibecker, D.; Etienne, M.;
Mathieu, R. Angew. Chem., Int. Ed. Engl. 1995, 34, 916.
[RuCl2(PPh3)(PAPF)] (1c). A solution of 13.2 mg of [RuCl2-
(PPh3)3] (0.014 mmol) and 6.2 mg of racemic PAPF (0.014 mmol)
was prepared in a NMR tube in toluene-d8. This tube was introduced
in the NMR probe and heated until 80 °C. After 1 h of reaction the
1H and 31P NMR detected the presence of the resonances of 1c,
which were assigned by comparing with the corresponding signals
1
of the starting materials and those of PPh3. H NMR (toluene-d8,
80 °C): 8.28 (2H, dd, JHH ) 7.8, JHP ) 11.2, HorthoPh-PAPF), 4.21
(Cp1), 4.12 (2H, Cp1), 3.84 (Cp2), 3.73 (Cp2), 3.66 (Cp2), 2.14
(Cp2,H5′); 3.10, 2.94 (NMe2) ppm. 13C{1H} NMR (toluene-d8, 80
°C): 136.80 (d, JCP ) 10.8, CorthoPh-PAPF), 75.26 (Cp1); 73.45
(Cp2,C5′), 72.00 (Cp2), 71.80 (Cp1), 71.10 (Cp2), 67.53(Cp2), 67.49
(Cp1), 55.74 (NCH3), 51.42 (NCH3), 42.42 (CH2), 38.35 (CH2) ppm.
31P NMR (toluene-d8, 80 °C): 82.9 (d, JCP ) 45.0, PAPF), 43.7
(d, PPh3) ppm.
[RuCl2(PPh3)(PAPF-c)] (2). [RuCl2(PPh3)3] (0.1534 g, 0.16
mmol) and racemic PAPF (80 mg, 0.176 mmol) were solved in 10
mL of toluene. This solution was introduced in a Fisher-Porter tube
(28) (a) Clark, G. R. J. Organomet. Chem. 1977, 134, 51. (b) Adams,
H. M.; Bailey, N. A.; Ridgway, C.; Taylor, B. F.; Walters, S. J.; Winter,
M. J. J. Organomet. Chem. 1990, 394, 349. (c) Bianchini, C.; Masi, D.;
Romerosa, A.; Zanobini, F.; Peruzzini, M. Organometallics 1999, 18, 2376.
(d) Wing-Wah, V.; Chu, B. W.-W.; Ko, C.-C.; Cheung, K.-K. J. Chem.
Soc., Dalton Trans. 2001, 1911. (e) Fillaut, J.-L.; de los Rios, I.; Masi, D.;
Romerosa, A.; Zanobini, F.; Peruzzini, M. Eur. J. Inorg. Chem. 2002, 935.
(29) Hallman, P. S.; Stephenson, T. A.; Wilkinson, G. Inorg. Synth. 1970,
12, 237.
(30) Hayashi, T.; Mise, T.; Fukushima, M.; Kagotani, M.; Nagashima,
N.; Hamada, Y.; Matsumoto, A.; Kawakami, S.; Konishi, M.; Yamamoto,
K.; Kumada, M. Bull. Chem. Soc. Jpn. 1980, 53, 1138.
(31) Jedlicka, B.; Widhalm, M.; Weissensteiner, W. Chem. Commun.
1993, 1329.

Formation of Fischer-Type Aminocarbenes
Organometallics, Vol. 25, No. 19, 2006 4503
and heated at 130 °C for 15 h. The solution was stirred during this
time. The resulting orange solution was transferred to a Schlenk
flask and evaporated to dryness. The resulting oil was triturated
with diethyl ether (2 × 5 mL), and an orange powder was obtained
(103 mg, 0.117 mmol, 73%). Monocrystals of 2 suitable for an
X-ray analysis were obtained by diffusion of diethyl ether into a
(90 °C); 18.5:100:28.8 (80 °C); 15.8:100:38.5 (60 °C). The
calculated constants were as follows: 271 (90 °C); 223 (80 °C);
106 (60 °C). The calculation of the equilibrium constants at 20
and 40 °C, by the same procedure, gives values practically identical
for the two temperatures and above those expected considering the
linear decay of Keq vs temperature followed by the preceding data.
As a consequence, we estimate that below 40 °C the equilibrium
is not achieved during the NMR time of the experiments.
The evolution of the stated solution was followed at 110 °C
during 6 h by 31P NMR spectroscopy. The corresponding resonances
of 2 (see below) were observed as minor signals. In addition, other
small resonances were observed such as two doublets of doublets
at 48.7 ppm (JPP ) 115.5, 36.6 Hz) and 36.1 ppm (JPP ) 115.5,
92.2 Hz) and a broad signal at about 45 ppm. These signals were
assigned to the intermediate species I.
X-ray Structure Determination. Orange crystals of C45H41Cl2-
FeNP2Ru‚2CH2Cl2 (complex 2) were obtained by diffusion of
diethyl ether into a CH2Cl2 solution of the complex. X-ray data
were collected on a Bruker Smart CCD area detector diffractometer
(graphite-monochromated Mo KR radiation, λ ) 0.71073 Å) by
0.3° ω-scan frames covering a complete sphere of the reciprocal
space.32 After data integration with the program SAINT, corrections
for crystal decay, absorption, and λ/2 effects were applied with the
program SADABS.32 The structure was solved with direct methods
using the program SHELXS-97.33 Structure refinement on F2 was
carried out with the program SHELXL-97.33 All non-hydrogen
atoms were refined anisotropically. Hydrogen atoms were inserted
in idealized positions and were refined riding with the atoms to
which they were bonded. Salient crystal data are as follows: C47H45-
Cl6FeNP2Ru, Mr ) 1055.40, orthorhombic, space group Pca21 (No.
29), T ) 223(2) K, a ) 24.633(5) Å, b ) 11.588(3) Å, c ) 15.585-
(4) Å, V ) 4448.7(19) Å3, Z ) 4, µ ) 1.133 mm-1. Of 62 074
reflections collected up to θ ) 30°, 12 798 were independent (Rint
) 0.042) and 11 000 were observed (I > 2σ(I)); number of refined
parameters: 524; final R indices: R1 ) 0.042 (all data), wR2 )
0.080 (all data).
1
CH2Cl2 solution of the complex. H NMR (DMSO-d6, rt): 8.93
(d, JH-P(PPh3) ) 4.4, -NdCH-); 8.70 (bm, HorthoPh-PAPF-c), 8.4,
7.9, 7.2, 7.1, 6.8 (bs, Ph); 7.6, 7.5, 7.4, 7.32, 6.95, 5.43 (t, JHH
)
8.3 HorthoPh-PAPF-c); 5.75, 4.36, 3.84, 3.13 (bs, Cp2); 4.85, 4.21,
3.39 (s, Cp1); 4.47 (d, JHH ) 12.2, H1′′); 3.73 (m, H2′′); 3.18 (s,
NMe); 2.63 (m, H3′′); 2.03 (m, H3′′); -3.62 (m, H2′′agost) ppm. 13C-
{1H} NMR (DMSO-d6, rt): 252.91 (t, JCP ) 14.6, -NdC(H)-);
141.04 (d, JCP ) 49.4, Cipso); 136.35 (d, JCP ) 9.2, Cortho); 134.38
(d, JCP ) 36.0, Cipso); 133.94 (d, JCP ) 19.5, Cortho); 134.38 (d, JCP
) 36.0, Cipso); 133.94 (d, JCP ) 19.5, Cortho); 132.73 (d, JCP ) 3.0,
Cpara); 132.18 (d, JCP ) 9.8, Cmeta); 131.55 (d, JCP ) 7.9, Cortho);
130.92 (Cpara); 129.6 (d, JCP ) 24.4, Cipso); 129.46 (d, JCP ) 11.6,
Cmeta); 129.44 (Cpara); 128.39 (d, JCP ) 9.2, Cmeta); 127.69 (d, JCP
) 9.8, Cmeta); Cp2: 87.81 (C1′), 73.17, 71.57, 71.11, 69.55; Cp1:
85.11 (d, JCP ) 11.6, C2); 76.85 (d, JCP ) 45.17, C1), 75.36 (d, JCP
) 5.5), 73.44, 71.66 (d, JCP ) 5.5); 64.38 (C1′′); 50.31 (NMe); 46.86
(t, JCP ) 16.5, C2′′); 25.53 (C3′′) ppm. 31P NMR (CDCl3, rt): 66.76
(d, JPP ) 34.2); 21.42 (d) ppm. Anal. Calcd for C45H41Cl2FeNP2-
Ru: C, 61.03; H, 1.58; N, 4.67. Found: C, 61.15; H, 1.63; N, 4.73.
Transformation of 2 into 3. Complex 2 (4 mg, 0.004 mmol)
was solved in 0.5 mL of DMSO-d6 in an NMR tube. At room
temperature no changes were observed. At 75 °C a new product,
1
3, appeared. After 2 h at 95 °C, the ratio 2:3 was 6:7. H NMR
data for 3: 11.00 (s, -NdCH-); 8.48 (dd, JHH ) 8.1, JHP ) 11.4,
HorthoPh-PAPF-c); 7.65-7.35 (m, Ph); 5.37 (s, Cp2); 4.94 (s, Cp1);
4.56 (d, JHH ) 12.1, H1′′); 4.41 (s, Cp2); 4.39 (t, JHH ) 2.6,Cp1);
3.94 (s, Cp2), 3.70 (s, Cp1); 3.64 (s, NMe); 3.61 (s, Cp2); -5.78
(bs, H2′′agost) ppm. 31P NMR (DMSO-d6, rt) data for 3: 31.44 (s)
ppm. MALDI mass spectra of a mixture of 2 and 3: m/z ) 850,
[RuCl(PPh3)(PAPF-c)]+; 673, [RuCl(DMSO-d6)(PAPF-c) + H]+;
452, [PAPF-c + H]+.
Acknowledgment. We gratefully acknowledge the Sub-
direccio´n General de Cooperacio´n Internacional for an “Accio´n
Integrada” project (HU-2003-0020) as well as O¨ sterreichischer
Akademischer Austauschdienst for the “Accio´n Integrada”
project 20/2004. Financial support from the Spanish DGES/
MCyT (CTQ2005-01430/BQU) and from the J. Castilla-La
Mancha-FEDER Funds (PBI-05-003) is acknowledged.
Determination of Equilibrium Constants for the Formation
of 1c and Monitoring of the Chemical Evolution of 1c to 2. The
equilibrium constant of the reaction [RuCl2(PPh3)3] + PAPF T
[RuCl2(PPh3)(PAPF)], 1c, + 2 PPh3 was determined at 60, 80, and
90 °C by monitoring the evolution of the different species by 31P
NMR spectroscopy. [RuCl2(PPh3)3] (18.8 mg, 19.6 mmol) and
PAPF (9.1 mg, 19.6 mmol) were suspended in 0.5 mL of toluene-
d8 in an NMR tube equipped with a Young valve. This sample
was first heated to 90 °C in the NMR probe. 31P NMR spectra,
with 240 scans, were recorded every 5 min during a total time of
105 min. The stabilization of the corresponding integrations was
achieved after 56 min. The same procedure was followed to
calculate the respective integrations at 80 and 60 °C, lowering the
temperature in the NMR probe. The equilibrium constants were
calculated, on the basis of the corresponding integrations, according
to the equation Keq ) [1c][PPh3]2/[RuCl2(PPh3)3][PAPF]. The 1c:
PPh3:PAPF ratios determined were the following: 21.9:100:28.4
Supporting Information Available: X-ray data of complex 2
in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
OM060314G
(32) Bruker, Programs SMART, version 5.054; SAINT, version 6.2.9;
SADABS version 2.03; XPREP, version 5.1; SHELXTL, version 5.1; Bruker
AXS Inc.: Madison, WI, 2001.
(33) Sheldrick, G. M. SHELX-97, Program System for Crystal Structure
Determination; University of Go¨ttingen: Go¨ttingen, Germany, 1997.